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Merged
youknowone merged 1 commit into from
May 16, 2026
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Use icu4x for casefold() #7780

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Use icu4x for casefold() 
For ASCII, casefold() is equivalent to lower casing the string.

Casefolding is a Unicode operation defined by the standard. Both CPython
and RustPython follow the standard without any frills. The icu4x set of
crates implement casefold as per the standard, so RustPython can use
the ICU crates instead of adding in a crate for one operation.

This also has the extra benefit of consistency - consistent Unicode
version and consistent crate usage.
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@joshuamegnauth54
joshuamegnauth54 committed May 15, 2026
commit 7884239b4c14650d6585b232efa25b559d5a4d3f
10 changes: 0 additions & 10 deletions Cargo.lock
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1 change: 0 additions & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,6 @@ bitflags = "2.11.0"
bitflagset = "0.0.3"
bstr = "1"
bzip2 = "0.6"
caseless = "0.2.2"

@ShaharNaveh ShaharNaveh May 15, 2026

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nice

chrono = { version = "0.4.44", default-features = false, features = ["clock", "std"] }
console_error_panic_hook = "0.1"
constant_time_eq = "0.4"
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1 change: 0 additions & 1 deletion crates/vm/Cargo.toml
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Expand Up @@ -73,7 +73,6 @@ strum_macros = { workspace = true }
thiserror = { workspace = true }
memchr = { workspace = true }

caseless = { workspace = true }
flamer = { workspace = true, optional = true }
half = { workspace = true }
psm = { workspace = true }
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37 changes: 24 additions & 13 deletions crates/vm/src/builtins/str.rs
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Expand Up @@ -45,10 +45,10 @@ use rustpython_common::{
hash,
lock::PyMutex,
str::DeduceStrKind,
wtf8::{CodePoint, Wtf8, Wtf8Buf, Wtf8Chunk, Wtf8Concat},
wtf8::{CodePoint, Wtf8, Wtf8Buf, Wtf8Concat},
};

use icu_casemap::TitlecaseMapper;
use icu_casemap::{CaseMapper, TitlecaseMapper};
use icu_locale::LanguageIdentifier;
use icu_properties::props::{
BidiClass, BinaryProperty, CaseIgnorable, Cased, EnumeratedProperty, GeneralCategory,
Expand Down Expand Up @@ -743,20 +743,31 @@ impl PyStr {
}
}

// casefold is much more aggressive than lower
// Case folding is a Unicode standard operation to erase case differences.
//
// Lower, upper, and title case are special properties. Case folding erases those
// differences. For ASCII, case folding is the same as lower case but other scripts have
// their own, well-defined mappings.
#[pymethod]
fn casefold(&self) -> Self {
match self.as_str_kind() {
PyKindStr::Ascii(s) => caseless::default_case_fold_str(s.as_str()).into(),
PyKindStr::Utf8(s) => caseless::default_case_fold_str(s).into(),
PyKindStr::Wtf8(w) => w
.chunks()
.map(|c| match c {
Wtf8Chunk::Utf8(s) => Wtf8Buf::from_string(caseless::default_case_fold_str(s)),
Wtf8Chunk::Surrogate(c) => Wtf8Buf::from(c),
})
.collect::<Wtf8Buf>()
.into(),
PyKindStr::Ascii(s) => s.to_ascii_lowercase().into(),
PyKindStr::Utf8(s) => CaseMapper::new().fold_string(s).to_string().into(),
PyKindStr::Wtf8(w) => {
let mut out = VecFmtWriter(Vec::with_capacity(w.len()));
let mapper = CaseMapper::new();
for chunk in w.as_bytes().utf8_chunks() {
mapper
.fold(chunk.valid())
.write_to(&mut out)
.expect("Writing to an in-memory buffer cannot fail.");
out.0.extend(chunk.invalid());
}
// SAFETY:
// * CaseMapper only produces valid UTF-8
// * Surrogates are appended as-is
unsafe { Wtf8Buf::from_bytes_unchecked(out.0) }.into()
}
}
}

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